Core-Shell Cathode Material for Lithium-Ion Battery Cycle Stability
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Solution Overview
Problem
High-nickel ternary cathode materials suffer from rapid decline in cycle performance due to conversion of surface high-valence Ni into halite phase during charging and discharging, and Mn and Co sources have non-uniform mixing and slow diffusion issues.
Innovation Solution
A cathode material with a core-shell structure is developed, where the inner core is rich in nickel and the outer shell is rich in cobalt and manganese, achieved through first roasting to form a manganese-rich surface and subsequent cobalt coating, controlling the gradients of Mn and Co elements to enhance safety, stability, and cycle performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a high-nickel ternary cathode material is used to improve capacity, then the capacity increases, but the cycle performance rapidly declines due to conversion of surface high-valence Ni into halite phase
Solution Approach 1:
The patent applies local quality by creating a core-shell structure where the inner core contains high-nickel content (0.8-0.95) for high capacity, while the outer shell contains lower nickel content (0.5-0.8) and higher cobalt and manganese content for stability. This spatial differentiation of composition allows the bulk material to maintain high capacity while the surface protects against degradation during cycling.
2Shape
If Mn and Co sources are mixed by solid phase method to form outer shell, then the shell structure is formed, but the mixing is non-uniform due to slow diffusion of Mn and segregation of Mn
Solution Approach 1:
The patent applies preliminary action by pre-coating the cobalt source onto the precursor particles before the first roasting step. This preliminary cobalt coating creates a template that guides subsequent manganese diffusion during roasting, ensuring uniform distribution of both elements in the outer shell and preventing manganese segregation that would occur with direct solid-phase mixing.
3Reliability
If a surface rich in both cobalt and manganese is formed to improve safety and stability, then the cycle performance improves, but the traditional methods cannot achieve simultaneous enrichment of both elements on the surface
Solution Approach 1:
The patent merges the cobalt coating step with the first roasting step by performing cobalt pre-coating followed immediately by roasting that simultaneously completes cobalt incorporation and manganese diffusion. This combined process achieves dual element enrichment in a single integrated operation rather than requiring separate steps for each element, simplifying manufacturing while achieving the desired surface composition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The cathode material exhibits improved capacity, safety, and cycle performance with reduced gas generation and heat release, and the preparation method ensures uniform distribution and diffusion of Mn and Co elements, enhancing first efficiency and rate performance.
Implementation Method 1
In the prior art, a Mn source and a Co source are mixed by a solid phase method, as Mn diffuses slowly and solid phase mixing is non-uniform
Implementation Method 2
a high-nickel ternary cathode material has a problem that surface high-valence Ni is converted into halite phase during charging and discharging
Data Source
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AI summary
The present invention relates to the technical field of lithium-ion batteries, and specifically to a cathode material and a preparation method therefor, a cathode plate, a lithium-ion battery and an electric device. Particles of the cathode material has a core-shell structure, wherein the core-shell structure includes a nickel-rich inner core and a lithium-nickel-cobalt-manganese-oxide outer shell coated on a surface of the nickel-rich inner core, wherein a nickel element content in the nickel-rich inner core is higher than a nickel element content in the lithium-nickel-cobalt-manganese-oxide outer shell; and a cobalt element content and a manganese element content in the lithium-nickel-cobalt-manganese-oxide outer shell are higher than a cobalt element content and a manganese element content in the nickel-rich inner core, respectively. The high nickel content in the inner core of the cathode material can improve capacity; the high manganese element in the outer shell can improve safety and stability of the cathode material, the high cobalt element in the outer shell can improve first efficiency and rate performance of the cathode material, and thus a manganese-rich and cobalt-rich outer shell effectively improves cycle performance of the cathode material and reduces gas generation and heat release.